1. Field of the Invention
The invention relates to the field of eyeglass lens production. More particularly, the invention relates to a device for retaining various laps for fining and polishing of lenses.
2. Prior Art
Ophthalmic and other types of lenses are typically produced from lens blanks of glass or plastic having two major surfaces, one of which is typically finished, and the other of which is unfinished. Cutting, fining, and polishing operations are performed on the unfinished surface of the lens blank by a machine responsive to data corresponding to a particular lens prescription. The cutting operations are usually accomplished by employing a ball mill for plastic lenses, or a grinder for glass lenses. These cutting operations generally create a lens surface closely approximating the shape of the finished lens. However, the cut surface of the lens blank is often rough and requires that subsequent fining and polishing operations be performed on the lens blank to achieve the requisite optical clarity.
The fining and polishing operations are ordinarily performed by engaging the cut surface of the lens blank with an abrasive surface having a shape that closely approximates the desired finished shape of the lens as defined by the lens prescription. This abrasive surface is referred to by those skilled in the pertinent art as a tool or xe2x80x9clapxe2x80x9d. During operation, the device to which the lens blank is mounted, moves the blank over the abrasive surface of the lap along a conforming contoured semi-spherical path, thereby fining and/or polishing the lens surface. Laps generally consist of two main components, a mounting surface or mandrel, and a removable abrasive pad that mounts on the mandrel and against which the lens blank is moved during fining and polishing operations. The shape of the mandrel must conform as closely as possible to the prescribed shape of the lens, therefore, different lens prescriptions require different laps to be used.
One drawback of prior art apparatuses is due to the mounting system for the various laps. Conventionally, laps are secured to a support by clamping a flange extending from the bottom edge of the lap. Clamping devices used include hydraulic, pneumatic and mechanical fasteners. All of these require a significant amount of time to install and therefore leave the art in need of a more time efficient yet reliable means of securing laps to the lap tower.
The above-identified drawbacks of the prior art are overcome or alleviated by the lap retaining mechanism of the invention.
The invention provides for quick change of laps and reliable failsafe retention thereof. This is beneficial in that many different laps are needed for the many different possible prescriptions for lenses.
The invention comprises a base through which a pair of shafts extend. The shafts are keyed to a pair of blades, one on each shaft. The blades rotate with the shafts because of the keyed relationship. The blades when not actuated (the failsafe condition) are rotated such that an outer aspect of each blade extends radially outwardly so that such outer aspect is received in a recess in a lap disposed on the lap tower to prevent separation of the lap from the tower. Upon actuation of a pneumatic, hydraulic, mechanical or electromechanical driver, a biasing means is overcome and the blades are retracted. In this condition the lap may be removed and replaced. Advantageously, the system provides a means for manual operation to be employed in the event that the mechanized drive is lost.
With the system of the invention significant time savings is realized during lens manufacture due to speedy lap changes.